<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=ul, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    /* 
        inline  块转换成为内联元素 
        block   内联转换成为块

        overflow :  溢出处理
         visible : 可以溢出
         hidden  ： 隐藏
         scroll  : 显示
         auto    : 根据内容来显示 
        overflow-x : 
        overflow-y : 
     */
    ul > li{display: block;}
    div{width:500px;height:200px;border:1px solid red;overflow-y: scroll;}
</style>
<body>
    <ul id="first">
        <li>A</li>
        <li>B</li>
        <li>C</li>
    </ul>
    <ul id="second">
        <li>A</li>
        <li>B</li>
        <li>C</li>
    </ul>

    <div>fdsafasfdasfasddddddddddddddddddddddddddddddddddddddddddddddddd</div>
</body>
</html>